This invention relates to clay slurries. In a particular aspect this invention relates to slurries of calcined clay and hydrite clay.
Kaolin is a fine, white clay, essentially a hydrated aluminum silicate, commonly known as hydrite clay which is used in large volume for the production of coatings, such as paper coatings and paints. Calcined kaolin is obtained by heating the naturally occurring hydrite to dryness. The calcined kaolin is brighter than the naturally occurring hydrite and contributes a higher degree of opacity to the coating. Once dehydrated, calcined clay does not revert to the hydrite form in the presence of water, but retains its advantageous properties.
Many pigments and extenders intended for use in water-based paints and coatings are shipped as high-solids aqueous slurries because of the economic advantages that accrue from bulk shipping and handling. However, calcined kaolin cannot be satisfactorily maintained as a high-solids slurry due to its tendency to readily settle out and cake. There is a need for a high-solids slurry, however, because it would make it possible to ship and handle the slurry like a liquid, thereby greatly reducing packaging and handling costs. The use of a slurry also reduces manufacturing time of the coating and eliminates the problem of dust fumes in the atmosphere.